Apparatus for forming thermoplastic composite materials

ABSTRACT

A composite with a thermoplastic matrix and fiber reinforcement is made by rotation of an exit die about a roving of continuous fiber in the presence of a thermoplastic melt. The rotation causes opposing inner and outer helical flow conditions which reduce the melt viscosity of the polymer by shear thinning while dragging and directing the polymer into the fiber roving thereby wetting and dispersing the fiber. A composite structure is formed with a polymer rich skin and a core region of unidirectionally aligned polymer and fiber. The polymeric skin is composed of helically aligned polymer chains which are coiled by the rotation around the core to compress the core region and enhance fiber wet out.

CROSS REFERENCE TO RELATED APPLICATION

This is a division of app. Ser. No. 08/933,454 filed on Sep. 18, 1997,now U.S. Pat. No. 6,258,453 and claims the benefit of Provisional app.Ser. No. 60/026,496 filed Sep. 19, 1996.

FIELD AND BACKGROUND OF THE INVENTION

This invention relates to composite materials formed by thermoplasticresins and reinforcing fibers. More particularly, this invention relatesto such composite materials and the process to form such materials,where the thermoplastic and fiber components impart great strength andcommercial utility to the composite compared with materials madepreviously to this invention.

The forming of composite materials using polymers and fibers has beenknown heretofore, and the processes, methods, apparatus, and productsrelating to such composites are disclosed in the patents of Montsinger(U.S. Pat. No. 5,176,775) and Cogswell (U.S. Pat. No. 4,541,884). Thedifficulties of wetting fiber with high viscosity thermoplastic resinsare well understood. Montsinger in '775 discloses a method of countercurrent flow between polymer and continuous fiber roving to increaseshear and lower viscosity of thermoplastic resin. Cogswell relies on lowviscosity polymers.

SUMMARY OF THE INVENTION

The present invention produces high strength, composite materials withthermoplastic polymer and reinforcing fiber. The thermoplastic polymermay have a high molecular weight resulting in a high viscosity. Thefiber may be continuous rovings of glass, carbon, metal, and/or organicfilaments. The commercial products of this invention may include longfiber reinforced thermoplastic compounds which are reformable andinjection molding pellets. Injection molding pellets have a fiber lengthequal to the pellet length, generally about 0.5 inches, and also have agenerally circular cross section with an aspect ratio (length/diameter)greater than 1. Another product of this invention is continuous fiberreinforced thermoplastic profiles which have a constant shape such as around rod and may be advantageously used in structural applications inplace of metal because of the relative low weight and high strength.

The polymer and fiber composite materials are produced in a fiber meltimpregnation process in which continuous filament fiber is contactedwith molten polymer and extruded or pultruded through a die orifice. Insuch a process, the exit orifice size of the die usually determines thefiber loading of the composite. For example, increasing the exit areaallows more polymer to pull through the die with a given fiber amountthereby lowering the fiber concentration. According to the presentinvention, relative rotation is imparted between the exit die and theadvancing polymer impregnated fiber. The relative rotation can beachieved, for example, by rotating the exit die about the axis of theadvancing fibers. This produces an unexpected increase in the fiberconcentration and the benefit of improved strength of the compositecompared to products made without rotation.

The exit die, preferably having a conical entrance and cylindrical exit,is rotated about the axially directed rovings of continuous fiber.Polymer melt is conveyed by pressure flow and/or fiber drag flow intothe orifice chamber. The rotation of the conical chamber wall induces aconihelical flow path for the polymer due to viscous drag from wettingof the wall by the polymer in addition to the axial drag by the fiber.The polymer flow path becomes helical in the cylindrical region of therotating orifice chamber. The difference in velocities and directionsbetween the polymer and fiber moving in an axial direction and thepolymer moving in a vortiginous, conihelical direction give rise to adispersive and impregnative shear to wet out fiber with polymer. Inaddition the polymer chains are coiled around the reinforcing, axiallydirected fiber and bound polymer to create a normal stress effect ofpolymer backflow. The velocity distributions are represented in FIG. 1as described in more detail below.

The present invention thus provides a method of producing a fiberreinforced thermoplastic material which comprises directing continuousfilaments along a predetermined advancing path of travel into andthrough an impregnation chamber. Molten thermoplastic polymer materialis injected from an extruder into the impregnation chamber and intointimate contact with the advancing filaments for wetting andimpregnating the filaments with the thermoplastic material. Thefilaments are then pulled through the exit die from the exit end of theimpregnation chamber while the exit die is rotated about the axis of theadvancing filaments.

The present invention also provides an apparatus for producing a fiberreinforced thermoplastic material, the apparatus including animpregnation chamber having an entrance end and an exit end. The exitend includes an exit die having a die opening. Means are provided fordirecting continuous filaments along a predetermined advancing path oftravel into and through the impregnation chamber so that the filamentsenter through the entrance end and exit through the exit die. Anextruder provides a supply of molten, thermoplastic polymer. Means isprovided for directing the molten thermoplastic material from theextruder into the impregnation passageway and into intimate contact withthe filaments. This promotes wetting and impregnation of the filamentswith the molten thermoplastic polymer. Means are provided for rotatingthe exit die about the axis of the filaments.

A fiber reinforced thermoplastic composite produced with this processand apparatus has a unique structure with a core region and a skinregion. The size of each region is related to the pulling speed andorifice rotation speed. The skin is composed only of polymer. Rotationof the orifice reduces the volume of polymer in the skin by contributingto the core region and normal stress polymer backflow. The core iscomposed of unidirectionally aligned fibers which are fully impregnatedwith the matrix thermoplastic polymer. The core polymer appears to bemore crystalline than the skin polymer probably because of slower,internal cooling. The polymer chains in the core are aligned with thefiber by the fiber drag. The skin is oriented by the helical flowalignment of the polymer chains. Shear strength measurements ofcomposite strands showed greater strength with increasing rotation speedat a given line speed and fiber concentration. Inner laminar shearstrength of the composite was also improved.

BRIEF DESCRIPTION OF THE DRAWINGS

The foregoing and other objects, features, and advantages of the presentinvention will be made apparent from the following detailed descriptionof the preferred embodiment of the invention and from the drawings, inwhich:

FIGS. 1A-1D are graphical illustrations of the polymer drag flow when acomposite material is formed according to the present invention;

FIG. 2 is a schematic illustration of an apparatus for producing a fiberreinforced composite according to the present invention;

FIG. 3 is a cross-sectional view of the impregnating chamber of theapparatus;

FIG. 4 is a fragmentary perspective view of an alternative embodiment ofapparatus adapted for processing multiple fiber strands simultaneously;

FIG. 5 is a schematic representation of a process in accordance with thepresent invention;

FIG. 6 is an enlarged fragmentary schematic view showing the passage offilaments through the exit die orifice;

FIG. 7 is an enlarged illustration of the gear mechanism for rotatingthe exit die according to an alternative embodiment;

FIG. 8 is a graphical representation of how the helix length iscalculated;

FIG. 9 is a cross-sectional illustration of a composite material formedaccording to the present invention;

FIGS. 10 and 11 are photographs of a cross section of composite materialunder polarized light; and

FIGS. 12-14 are graphs showing the effect of die rotation and otherfactors on the properties of the composite material.

DETAILED DESCRIPTION OF THE INVENTION

The present invention will now be described more fully with reference tothe accompanying drawings, in which preferred embodiments of theinvention are shown. The invention should not, however, be construed aslimited to the specific embodiments set forth herein. The specificembodiments are provided so that this disclosure will be thorough andcomplete and will fully convey the scope of the invention to thoseskilled in the art.

The process according to the present invention combines drag flow fromthe fiber pulling the polymer through the exit die with conihelical andhelical drag flow due to the exit die rotation. Pressure flow may alsoexist due to exit die restriction creating back flow. The combination ofopposing inner, forward and outer backward helical and conihelical flowsservers to lower viscosity and to increase the wet out of fiber by thepolymer.

In FIG. 1A, the axial drag flow z of polymer by the fiber isrepresented. The polymer flow velocity is highest at the fiber anddiminishes out to the exit die wall (since the wall has no velocity inthe z direction). In FIG. 1B the tangent flow created by the exit dierotation is shown. FIG. 1C shows the drag flow combined with theresulting normal stress back flow as the polymer is squeezed around thefiber. Finally, FIG. 1D shows the combined velocity distributions of thedrag, tangent, and normal stress pressure flows that exist when theprocess is operating to produce the inner forward (+y, +z) and outerbackward (+y, −z) helical and conihelical flows.

The apparatus according to the present invention incorporates some ofthe features of the apparatus according to U.S. Pat. Nos. 5,176,775 and5,447,793, to Lawrence V. Montsinger, which are fully incorporatedherein by reference. The apparatus, generally indicated at 10 in FIG. 2,has fiber supply means 11, preferably in the form of a creel mounting aplurality of packages of fiber material for supplying continuousfilament fiber 12; advancing means for advancing the fiber 12 from thecreel along a predetermined path of travel; a heater 13 disposed alongthe predetermined path of fiber travel for heating advancing fiber to apredetermined elevated temperature; an extruder 14 for supplying molten,heated thermoplastic material and an impregnation chamber 15 disposedalong the predetermined path of fiber travel and connected to theextruder 14 for receiving a flow of molten heated thermoplasticmaterial. The thermoplastic material is directed through theimpregnation chamber in a direction opposite to that of the advancingfiber so that it impregnates and surrounds the advancing heated fiber.Shear forces arising between the advancing heated fiber and the flow ofthermoplastic material promote wetting of the fiber by and impregnationof the fiber by the thermoplastic material.

As best illustrated in FIG. 3, fibers 12 enter the upper end of theimpregnation chamber 15 and are guided along a vertical impregnationpassageway 20. As the fibers advance along their path, thermoplasticmaterial from the extruder passes to the vertical impregnationpassageway. The passageway 20 is arranged for downward passage of fibers12 therethrough and for upward movement of thermoplastic material and isheated by appropriate means. The countermovement gives rise to shearforces between the advancing heated fiber and the directed flow ofthermoplastic material which, in accordance with this invention, promotewetting of the fiber by an intimate impregnating enclosure of the fiberand the thermoplastic material. Additionally, the path along which thefiber 12 is guided within the impregnation column 20 is such as to causethe thermoplastic material entrained in downward movement to be squeezedbetween the fibers.

At the foot of the column 20, the continuous filament fibers 12 arepassed about a single turning guider bar 21 which thereby requires thatthe fibers come to a single plane. The gradual converging of the fibersmoving downwardly force the molten thermoplastic material into the spacebetween the filaments and then squeezes the thermoplastic material intointimate contact with the fibers, assisting in assuring wetting of thefibers with the thermoplastic. Continuous fiber is pulled through anorifice in the form of an exit die 22 as a band, web, tow, or roving.The exit die 22 diameter regulates the amount of polymer that is pulledout of a die by the fiber. The exit die area controls the polymer tofiber ratio.

The exit die 22 is shown generally in FIG. 3 and is shown in more detailin FIGS. 6 and 7. As shown in FIG. 6, the exit die includes a conicalentrance end 23 and a exit end 24 with a cylindrical bore. Morespecifically, the conical entrance 23 is frustoconical and tapers tomeet the cylindrical exit 24 portion. The conical region 23 of the exitdie 22 forms a vortiginous flow path due to drag by the exit die surfacewhen the exit die is rotated. The conical region 23 may have aconihelical, heliconical, or helicoidal shape. The portion of the exitdie 22 in which the diameter is constant forms a cylinder and creates ahelical flow path when the exit die rotates. A right hand or left handhelix length is defined by the hypotenuse of the circumference and thelead (land length). Increasing the length of the cylindrical portion 24simulates the effect of reducing line speed which reduces the pitch andimproves the product in terms of wet out, shear strength, etc. Thelength/diameter ratio may be varied from 0.01 to 1000 and, preferably,from 4.4 to 10.6.

As to the conical portion 23 of the exit die 22, the tapered anglethereof may range from 0 to 90 degrees, preferably from 5 to 10 degrees.An angle within the range of 4 to 6 degrees has been found useful forcertain applications. A smaller angle requires a longer taper length forthe cone region. The total angle formed is generally two times the taperangle. Changing the taper angle changes the conihelical velocityrelative to the linear velocity in the pulling direction. Theconservation of angular momentum about a fixed axis requires a change invelocity which implies an acceleration constant. velocity is anotherterm for shear rate, therefore the taper offers a constant change inshear rate.

The surface energies of the exit die and polymer determine the amount ofpolymer drag (or friction flow) by the exit die rotation. A highcoefficient of friction (rough surface) is desirable. A range from 0.1to 1.0 is desired. Patterns may be cut into the exit die surface (suchas a screw thread) which may influence the flow path of the polymer.Other methods to influence the polymer flow path and/or createturbulence to wet out fiber may include directional jets to injectpolymer into a vortex.

Fiber may spread to a width greater than the exit die entrance or exitdiameter due to the rotational drag. The spread is in multipledimensions. As the fiber brushes against the exit die wall, oppositionto the rotational drag may create a pressure gradient for polymer topenetrate the fiber bundle.

According to the illustrated embodiment, the exit die 22 rotates aboutthe axis of the advancing fibers 12. The exit die is rotated by asuitable drive assembly, such as intermeshing gears 31, 32 and motor 33,as illustrated in FIG. 6. The positioning guide 21 directs the fibers 12into the high shear peripheral zone of the exit die wall. Thepositioning guide 21 also prevents the fiber from twisting before wetout. However, some twisting after wet out may desirably squeeze polymerthrough the filaments to enhance wet out. Thus, according to an optionalaspect of the invention, the polymer impregnated filaments may berotated at a location downstream from the exit die 22 by a suitabledevice, such as by the canted puller belt system 16 as illustrated inFIG. 2, which includes a pair of drive belts 16a, 16b mounted at anangle to one another. Rotation of the filaments causes twist to back upinto the die, thus imparting relative rotation between the advancingpolymer impregnated filaments and the die surface. The die may bestationary in this instance or may be rotated in the same or oppositedirection as the filaments.

Rotating the exit die around the fiber and also optionally rotating ortwisting the fiber within the exit die changes the ratio of polymer tofiber. As the rotation increases, the fiber concentration increases.Rotational speeds may vary from 0 to 10,000 rpm, preferably less than600 rpm. Rotation speed and line speed define a lead or pitch, measuredas inches per min/rev. per min (inches/revolution). At 0 rpm the pitchis infinite. The pitch may be between 0 and infinity, preferably between0.001 to 1,000.

When the exit die is rotated, the shear stress and the shear rate areincreased. The shear develops two components from the axial andtangential forces. The shear rate increases through vector addition ofthe velocity and the rotational speed. The corresponding shear stresssees the pulling force of the fiber combined with the rotational forceor torque. Viscosity is defined as the shear stress divided by the shearrate. For pseudoplastic polymers the viscosity is lower at higher shearrates due to shear thinning. A shear rate range between 1 and 100,000sec-1 would cover most cases. The rotation of the die orients thepolymer chains which wrap around and compress the core resin and fiber.This strangulating effect creates a normal stress which improves fiberwet out and increases the fiber concentration. Rotation of the fiber(strand) in a stationary exit die using canted puller belts may have asimilar effect as exit die rotation.

By controlling the exit die temperature it is possible to allow forcooling of the composite to occur in the helical zone while stillimparting shear by rotation to strain and further orient the skinpolymer. As shown in FIG. 4, the apparatus may be equipped with multipleexit dies, each connected for rotation with intermeshing gears to allowfor more strands to be produced. In the configuration shown in FIG. 7,the exit die rotational direction alternates with each successiveposition. Clockwise and counterclockwise directions have the same effecton wet out and fiber concentration.

Polymer chains tend to align in the direction of shear and flow. Theflow path of the polymer and the direction of the chain alignment aredescribed by the helix shown in FIG. 8. By definition a helix isgenerated by a point moving around and along the surface of a cylinderor cone with a uniform angular velocity about the axis, and with auniform linear velocity in the direction of the axis. The distancemeasured parallel to the axis traversed by the point in one revolutionis called the lead or pitch. The ratio of line speed to rotation speeddefine the lead of the helix. Improved wet out, fiber dispersion, strandintegrity, mechanical properties and higher fiber concentration areobserved with increasing rotation speed at constant line speed (i.e.shorter lead).

The thermoplastic polymers may be crystalline, amorphous, orsemicrystalline. The high molecular weight, high viscosity,thermoplastic polymers may include but are not limited to:

polyolefins such as PP, LDPE, and HDPE

polyamides such as nylon 6, nylon 66,

nylon 46, Nylon 11

polyesters such as PET, PET, PCT, and

PTT, polyarylates

thermoplastic polyurethanes

PC, PEI, PES, PPS, PEEK, PVC, CPVC, PAI,

POM, PS, PVA, PMMA,

PAEK, PAS, PI, PPO, PTFE

Fiber roving may include glass, carbon, organic, and metal types ofcontinuous or semicontinuous fiber.

An interesting feature of the invention is the change in fiberconcentration which occurs as the rotation speed increases at a constantline speed. The mechanism for this may be a Weissenberg normal stresseffect. This is a tendency for a viscoelastic fluid to flow in adirection normal to the shear stress. As the polymer chains are coiledabout the axially directed fiber the strangulating effect would likelyforce polymer along the fixed core axis relative to the rotating wall ofthe cylinder. The normal stress flow direction is back into the diesince the fiber concentration increases and the composite would offerresistance. The exit die restriction would also contribute to the backflow pressure.

The melt viscosity of the thermoplastic resin is influenced by molecularweight, temperature, and shear rate. A pseudo plastic, non-Newtonianpolymer will experience shear thinning or viscosity reduction withincreasing shear rate. A desirable feature of this invention is theincreased shear rate induced by the exit die rotation which lowers themelt viscosity of high molecular weight thermoplastic. Fiber is easierto wet out with thermoplastic at lower melt viscosity.

In Volume I of Fluid Mechanics by Bird, Armstrong, and Hassager, p. 159,(TA357D95) a mathematical description of the shear rate for steadyhelical flow is proposed in which both the strand velocity and therotational velocity contribute to the shear rate. The shear rate wasestimated to be about 100 sec-1 at 0 rpm and 10,000 sec-1 at 600 rpm andviscosity varied from 500,000 cp to 10,000 cp in the trials with thisinvention.

Benefits of the composite material according to the present inventioninclude a unidirectional fiber alignment for higher tensile strength,longer fiber length for improved stress transfer efficiency leading tohigher modulus, and fewer fiber ends which reduce the number of stressrisers and increase impact strength. As seen in FIG. 9, the compositematerial C is characterized by having a thermoplastic resin rich skinregion 41 which surrounds a core region 42 containing unidirectionallyaligned fibers 12 in a matrix of thermoplastic polymer. The smooth,resin rich skin region is created by the rotational effect at the diesurface. In the skin region, the morphology of the polymer ischaracterized by the polymer molecules or chains being oriented oraligned along a helical path. The skin polymer is less crystalline andmore amorphous than the core polymer. The skin allows long fiber pelletsto be cut to shorter lengths without compromising (breaking open) thepellet form. The core polymer chains are generally aligned with thefiber. The skin region may constitute from 20 to 80% of the volume ofthe composite. The differences in the molecular orientation of thepolymer chains in the skin region and in the core region may beascertained by viewing the regions of the sample under polarized lightusing a polarizing filter. Birefringence measurements may also beemployed.

Composite long fiber pellets made by rotation may be characterized bythe length of fiber filaments being equal to or greater than the pelletlength. The length of a pellet may range from 0.125 inches to about 1.0inches and the diameter may range from about 0.125 to about 0.5 inchesso that the aspect ratio (length/diameter) may range from 0.25 to 4.0.The number of glass fiber filaments range from 2,000 to 16,000 in apellet and up to 65,000,000 in a profile.

The helical orientation of polymer chains wrapped around the core resinand fiber produce a unique structure. As the rotation speed increasesthere is greater strangulation of the core region. The boundary of thecore becomes more distinctive and circular.

A distinctive feature of the composite, illustrated schematically inFIG. 9, is the smooth, resin rich surface created by the die rotation.As the exit die rotates a resin rich skin forms on the composite. Thepolymer impregnated fiber rovings are positioned in the core region ofthe composite. The core polymer is dragged by the fiber and oriented inthe same direction as the fiber. The skin and core regions aredistinctively formed. The skin forms a ring around the core while thecore forms a circular shape. FIG. 10 shows the cross section of acomposite illuminated with polarized light and magnified 10×. The samplefrom Run 656-1 contains two rovings made at 0 rpm. The rovings areformed into U shapes and the fiber concentration is 47.1 percent. Theskin core area ratio of sample 656-1 is about 1.1. FIG. 11 shows thecross section of sample 656-4 made with two rovings at 320 rpm. Fiberconcentration has increased to 59.2 percent. The core area ratio ofsample 656-4 rpm is 0.65. Fiber loading may range from 5 to 80 percentby weight of the composite, more particularly 20 to 80 weight percent.Good results have been observed at fiber concentrations from 30.4 to68.7 weight percent. The illumination of the skin under polarized lightis much brighter, suggesting an amorphous polymer structure. The core isless bright, suggesting a more crystalline structure.

The structure of the skin consists of the helically aligned polymerchains and may generally occupy up to 60 percent of the cross section ofthe composite. Higher molecular weight polymers generally have longerpolymer chains and are characterized by low melt flow rates (ASTMD1248). The longer chain polymers would have greater advantage incompressing the core. The polymer chains are drawn along the helixformed by the simultaneous exit die wall rotational drag and the axialdrag by the fiber. The helical alignment of the skin polymer chainsimproves the inner laminar shear strength of the strand which allowslong fiber pellets to be cut to short lengths without compromising andbreaking open the pellets. The skin also provides lubricity whichprotects the fiber in a subsequent handling and molding and preservesfiber length.

By cooling the rotating exit die, some cooling of the strand may occurin the region of the rotating die. This increases orientation bydragging the solidifying resin at a temperature below the melting point.Polymers may be crystalline, amorphous, or both (semicrystalline)depending on the structural regularity. Condensation polymers such aspolyamides and polyesters are crystalline. Addition type polymers suchas polycarbonate and polyetherimide are amorphous. Polypropylene issemicrystalline. The cooling rate will influence the amount ofcrystallinity.

The fiber yield is defined as the length per unit weight in yards/lb. Atypical E glass roving is 225 yards/lb. and contains about 4,000filaments. The exit die rotation improves fiber dispersion and wet outand in turn allows for more fiber rovings to be incorporated into thecomposite. Increasing the number of rovings in a strand for long fiberpelletizing while holding the fiber concentration and line speedconstant results in greater output and improved production economy. Theyield (yd/lb.) of the fiber was varied from 225 to 56 in long fibercompounding. A range from 2,000 to 0.01 yd/lb. is desired. Both insidepull and outside pull fiber is applicable.

The dispersion pattern of fiber formed by the turning guide istransformed by the exit die rotation. The composite cross sections inFIGS. 10 and 11 show the rotational influence at 0 and 320 rpm on thefiber core. The U shape fiber pattern in FIG. 10 is transformed into afuzzy, circular core of dispersed fiber and polymer in FIG. 11.

EXAMPLES

A series of experiments was performed to study the effects of rotationon the composite properties. A summary of the data is shown in Table 1.The relationships between fiber concentration, rotational speed, pitch,and shear strength are shown in FIGS. 12 and 13. A relationship betweenmelt viscosity and rotation speed is shown in FIG. 14.

Table 1 shows the relationship between the process conditions of fiberyield, exit die diameter, line speed, and rotation speed on fiberconcentration, shear strength, and viscosity for polypropylene and glassfiber. Long fiber pellets were produced with 1, 2, and 4 rovings at0.113, 0.136, and 0.250 inch hole sizes. Die rotation was varied from 0to 600 rpm.

The influence of rotation speed and the ratio of line speed to rotationspeed (i.e. lead or pitch) on fiber concentration was plotted in thegraph of FIG. 12. The fiber concentration was measured with an ashingfurnace. Shear strength measurements were made on composite strandsusing an Instron tensile tester according to ASTM D 512. The change inshear strength of the composite at similar fiber concentrations wasplotted in the graph of FIG. 13. The melt viscosity of the polypropylenewas estimated from the pressure, exit die geometry, line speed, androtation speed and plotted in the graph of FIG. 14.

Run No

652. A comparison was made between a stationary die and a die rotated at80 rpm. Fiber concentration increased from 30.4 to 37.4 percent.

653. The die was rotated from 0 to 80 rpm in increments of 20 rpm. Fiberincrease from 32.7 to 40.3.

654. Line speed was doubled to 30 fpm. Die speed was increased from 0 to80 rpm. Fiber content increased from 31.9 to 37.3 percent.

655. Line speed was evaluated at 15 and 30 fpm. Die speed was increasedfrom 0 to 320 rpm. Fiber increased from 32.7 to 46.2 percent at 15 fpmfrom 0 to 320 rpm. Fiber increased to 45.1 at 30 fpm, 320 rpm.

656. Fiber yield was changed from 225 to 112 yd/lb. by running tworovings. Die speed was increased from 0 to 320 rpm at 15 fpm. Fiberconcentration increased from 47.1 to 59.2 percent. Doubling line speedto 30 fpm reduced fiber concentration to 55.4 percent at 320 rpmconfirming the inter relation of line speed and rotation speed.

657. Clockwise and counterclockwise rotations were evaluated. Nodifference was observed.

659, 660. Die land length was varied from 0.7 to 1.2 inches for a 0.113inch diameter. L/D ratios were 6.2 and 10.6. Increasing the L/D ratiogenerally increased fiber concentration and shear strength.

674,675,676. Die hole diameter was increased to 0.250 inches and thenumber of rovings was increased to 4. Land lengths of 1 and 4 incheswere evaluated. Rotational speed was increased to 600 rpm. Fiberconcentration increased from 34.0 to 45.7% in Run 674.

While particular embodiments of the invention have been described, itwill be understood, of course, S the invention is not limited theretosince modifications may be made by those skilled in the art,particularly in light of the foregoing teachings. It is therefore,contemplated by the appended claims to cover any such modifications thatincorporate those features of these improvements in the true spirit andscope of the invention.

TABLE I DIE ROTATION TRIAL SUMMARY Die 26 Aug. 1996 Run Linespd RotationPitch Yield Ash (cal) Area Die Hole Die Land No. ID Dir (fpm) (rpm)(in/rev) (yd/lb) (wt %) (in) (sq in) (in) (in) 652 1 CW 15 0 225 30.40.1148 0.01035 0.136 0.60 2 CW 15 80 2.25 225 37.4 0.1004 0.00792 0.1360.60 653 1 CW 15 0 225 32.7 0.1096 0.00943 0.136 0.60 2 CW 15 20 9.00225 35.2 0.1045 0.00858 0.136 0.60 3 CW 15 40 4.50 225 36.6 0.10190.00816 0.136 0.60 4 CW 15 60 3.00 225 37.7 0.0999 0.00784 0.136 0.60 5CW 15 80 2.25 225 40.3 0.0955 0,00716 0.136 0.60 654 6 CW 30 0 225 31.90.1113 0.00973 0.136 0.60 7 CW 30 20 18.00 225 34.2 0.1065 0.00891 0.1360.60 8 CW 30 40 9.00 225 35.2 0.1045 0.00858 0.136 0.60 9 CW 30 60 6.00225 36.1 0.1028 0.00830 0.136 0.60 10 CW 30 80 4.50 225 37.3 0.10060.00795 0.136 0.60 655 1 CW 15 0 225 32.7 0.1096 0.00943 0.136 0.60 2 CW15 80 2.25 225 39.4 0.0970 0.00739 0.136 0.60 3 CW 15 160 1.13 225 42.90.0915 0.00658 0.136 0.60 4 CW 15 320 0.56 225 46.2 0.0868 0.00592 0.1360.60 5 CW 30 320 1.13 225 45.1 0.0883 0.00612 0.136 0.60 6 CW 30 1602.25 225 42.1 0.0927 0.00675 0.136 0.60 7 CW 30 80 4.50 225 39.2 0.09730.00744 0.136 0.60 656 1 CW 15 0 112 47.1 0.1214 0.01158 0.136 0.60 2 CW15 80 2.25 112 53.2 0.1108 0.00984 0.136 0.60 3 CW 15 160 1.13 112 56.20.1062 0.00886 0.136 0.60 4 CW 15 320 0.56 112 59.2 0.1018 0.00814 0.1360.60 5 CW 30 320 1.13 112 55.4 0.1074 0.00906 0.136 0.60 657 1 CCW 15 802.25 112 51.8 0.1131 0.01005 0.136 0.60 2 CCW 15 80 2.25 112 51.9 0.11300.01003 0.136 0.60 3 CCW 15 240 0.75 112 56.2 0.1062 0.00886 0.136 0.604 CCW 15 160 1.13 112 55.0 0.1080 0.00916 0.136 0.60 5 CCW 30 320 1.13112 54.9 0.1082 0.00920 0.136 0.60 6 CCW 7.5 320 0.28 112 59.8 0.10100.00801 0.136 0.60 659 1 CCW 15 0 112 60.0 0.1007 0.00796 0.113 1.20 2CCW 15 160 1.13 112 65.3 0.0937 0.00690 0.113 1.20 3 CCW 15 320 0.56 11268.7 0.0896 0.00631 0.113 1.20 4 CCW 7.5 320 0.28 112 68.2 0.09020.00639 0.113 1.20 5 CCW 30 320 1.13 112 66.4 0.0924 0.00671 0.113 1.20660 1 CCW 15 0 112 57.4 0.1044 0.00856 0.113 0.7 2 CCW 15 160 1.13 11261.2 0.0991 0.00771 0.113 0.7 3 CCW 15 320 0.56 112 63.9 0.0955 0.007160.113 0.7 4 CCW 30 320 1.13 112 62.2 0.0977 0.00750 0.113 0.7 5 CCW 30320 1.13 112 61.9 0.0981 0.00756 0.113 0.7 6 CCW 15 320 0.56 112 63.70.0956 0.00718 0.113 0.7 7 CCW 15 160 1.13 112 61.3 0.0989 0.00768 0.1130.7 674 1 CCW 13.3 300 0.53 56 43.6 0.250 1.00 2 CCW 14.6 0 56 38.50.0000 0.00000 0.250 1.00 3 CCW 14.6 150 1.17 56 34.0 0.0000 0.000000.250 1.00 4 CCW 14.4 300 0.58 56 34.8 0.0000 0.00000 0.250 1.00 5 CCW14.5 300 0.58 56 42.3 0.0000 0.00000 0.250 1.00 6 CCW 14.5 300 0.58 5645.7 0.0000 0.00000 0.250 1.00 675 1 CCW 20 580 0.41 56 38.6 0.00000.00000 0.25 1 2 CCW 20 580 0.41 56 42.6 0.0000 0.00000 0.25 1 3 CCW 20290 0.83 56 38.6 0.0000 0.00000 0.25 1 4 CCW 9.2 600 0.18 56 35.5 0.00000.00000 0.25 1 674 1 ccw 24 568 0.51 56 51.4 0.0000 0.00000 0.25 4 2 ccw16.5 608 0.33 56 50.6 0.0000 0.00000 0.25 4 3 ccw 18 600 0.36 56 58.90.0000 0.00000 0.25 4 4 ccw 18 600 0.36 56 57.3 0.0000 0.00000 0.25 4 5ccw 18 600 0.36 56 47.8 0.0000 0.00000 0.25 4 6 ccw 24 600 0.48 56 48.10.0000 0.00000 0.25 4 Mod Run Pres Visc Load Pk Stron (psi) Strain No.ID Dir. L/D (psi) (cp) (lbs) (psi) ×10⁻⁶ (%) 652 1 CW 4.4 36 2 CW 4.4 34173,891 653 1 CW 4.4 18 24,666 1.36 2.93 2 CW 4.4 21 429,613 3 CW 4.4 21214,806 4 CW 4.4 18 122,746 5 CW 4.4 21 107,403 33,103 1.49 2.82 654 6CW 4.4 36 215.3 22,124 0.91 3.71 7 CW 4.4 30 613,732 250.2 28,088 1.243.48 8 CW 4.4 36 368,239 233.2 27,183 1.33 3.26 9 CW 4.4 30 204,577255.9 30,832 1.54 3.12 10 CW 4.4 30 153,433 234.7 29,525 1.52 3.14 655 1CW 4.4 36 241.5 25,600 1.29 2.41 2 CW 4.4 33 168,776 3 CW 4.4 30 76,717232.2 35,309 1.75 2.69 4 CW 4.4 30 38,358 209.3 35,370 1.70 2.55 5 CW4.4 42 53,702 201.6 32,914 1.74 2.02 6 CW 4.4 45 115,075 204.3 30,2661.41 2.83 7 CW 4.4 42 214,806 227.5 30,597 1.50 2.73 656 1 CW 4.4 42351.6 30,377 1.89 2.59 2 CW 4.4 36 184,120 336.8 34,933 1.70 3.51 3 CW4.4 36 92,060 337.3 38,082 2.15 3.25 4 CW 4.4 36 46,030 321.9 39,5501.98 3.06 5 CW 4.4 69 88,224 329.2 36,336 1.97 3.17 657 1 CCW 4.4 45230,150 2 CCW 4.4 39 199,463 3 CCW 4.4 36 61,373 354.8 40,050 2.51 2.884 CCW 4.4 36 92,060 309.4 33,772 2.83 2.14 5 CCW 4.4 75 95,896 303.633,015 2.30 2.66 6 CCW 4.4 18 23,015 331.5 41,376 1.92 2.79 659 1 CCW10.6 45 275.5 34,586 2.07 2.85 2 CCW 10.6 28 29,746 361.0 35,999 1.933.03 3 CCW 10.6 39 20,716 294.5 46,708 1.52 2.71 4 CCW 10.6 24 12,748288.4 45,137 2.86 2.42 5 CCW 10.6 63 33,465 263.3 39,265 2.44 2.84 660 1CCW 6.2 36 285.6 33,366 2.00 2.65 2 CCW 6.2 33 60,100 290.8 37,699 2.272.81 3 CCW 6.2 30 27,318 299.0 41,712 2.61 2.72 4 CCW 6.2 63 57,368270.6 36,095 2.26 2.93 5 CCW 6.2 66 60,100 6 CCW 6.2 30 27,318 7 CCW 6.230 54,636 674 1 CCW 4.0 30 45,127 2 CCW 4.0 22 3 CCW 4.0 39 117,331 4CCW 4.0 61 92,210 5 CCW 4.0 31 46,632 6 CCW 4.0 26 39,110 675 1 CCW 4.045 2 CCW 4.0 30 23,342 3 CCW 4.0 33 51,352 4 CCW 4.0 33 24,820 674 1 ccw16.0 43 8,541 2 ccw 16.0 43 7,979 3 ccw 16.0 54 10,116 4 ccw 16.0 5297,21 5 ccw 16.0 54 10,154 6 ccw 16.0 54 10,154

That which is claimed is:
 1. An apparatus for producing a fiberreinforced thermoplastic material comprising: an impregnation chamberhaving an entrance end and an exit end, the exit end including an exitdie; means for directing continuous filaments along a predeterminedadvancing path of travel into and through said impregnation chamber,entering through said entrance end and exiting through the exit die; anextruder for providing a supply of molten, thermoplastic polymer; meansfor directing molten thermoplastic material from said extruder into theimpregnation passageway and into intimate contact with the filaments topromote wetting and impregnating of the filaments with the moltenthermoplastic polymer; and means for imparting relative rotation byrotating the exit die about the axis of the advancing filaments.
 2. Anapparatus according to claim 1 wherein said means for imparting relativerotation further comprises means located downstream of the exit die forrotating the advancing resin impregnated filaments.
 3. An apparatusaccording to claim 1 comprising means on the downstream side of saidexit die for pulling the polymer impregnated filaments from theimpregnation chamber and through said exit die.
 4. An apparatusaccording to claim 1 wherein said molten polymer is directed into theimpregnation chamber at a location adjacent said exit end thereof sothat the molten polymer flows toward said entrance end incounter-current relation to the direction of movement of the advancingfilaments and in intimate contact with the filaments whereby shearforces arising between the advancing filaments and the flow ofthermoplastic material promote wetting and impregnation of the filamentswith the molten thermoplastic polymer.
 5. An apparatus according toclaim 1 wherein said exit die is provided with a conical entrance and acylindrical exit.
 6. An apparatus according to claim 5 wherein theconical entrance of the exit die has a length to diameter ratio between0.01 to 1,000.
 7. An apparatus according to claim 6 wherein the lengthto diameter ratio is between 4.4 to
 16. 8. An apparatus according toclaim 1 including means for engaging and turning the advancing filamentswhile in the impregnation chamber.
 9. An apparatus according to claim 1wherein said means for rotating the filaments comprises canted pullerbelts.
 10. An impregnation apparatus to impregnate continuous filamentswith molten thermoplastic material comprising: an impregnation chamberfor receiving molten thermoplastic material having an entrance end toreceive said filaments and an exit end, the exit end including at leastone rotatable exit die; wherein said at least one rotatable exit diecontains a gear engagable to a drive gear to rotate the exit die aboutthe axis of said filaments that pass therethrough.
 11. The apparatus ofclaim 10 wherein the at least one rotatable exit die contains a conicalentrance and a cylindrical exit.
 12. The apparatus of claim 11 whereinthe conical entrance of the at least one rotatable exit die has a lengthto diameter ratio of 0.01 to
 1000. 13. The apparatus of claim 12 whereinthe length to diameter of the conical entrance is between 4.4 and 16.14. The apparatus of claim 10 wherein the at least one rotatable exitdie includes a die opening of predetermined size selected to provide aratio of thermoplastic polymer to filaments in the range of about 0.25to 1.0 to about 4.0 to 1.0.
 15. An apparatus, comprising: animpregnation chamber to receive at least one continuous filament rovingand having an entrance end and an exit end, the exit end including atleast one rotatable exit die; an extruder for providing a supply ofmolten thermoplastic polymer to said chamber; and a puller for pullingsaid at least one filament roving through said chamber and through saidat least one exit die, and wherein said at least one rotatable exit diecontains a gear engagable to a drive gear to rotate the exit die aboutthe axis of said at least one roving that passes therethrough.